by Cathy Payne, USA TODAY

by Cathy Payne, USA TODAY

This year's spring allergy season is nothing to sniff at: The season may be longer and stronger, allergists say.

Blooming trees have been releasing pollen into the air, triggering allergic reactions in some people. The start of tree pollination varies across the country, and cold spells in certain regions cause pollen levels to fluctuate.

Some people who are sensitive to tree pollen also may feel the effects of grass pollen as spring gives way to summer. They may get a break before ragweed pollen hits in the fall.

Many people with spring and summer allergies may not get relief until July, when it gets very hot and pollen counts go down, says William Berger, an adviser for the Asthma and Allergy Foundation of America.

The higher pollen levels may worsen symptoms for some people, but effects vary among individuals, says Weber, an allergist in Denver.

With an allergy, the immune system overreacts to a trigger substance, or allergen. Outdoor allergies (also known as seasonal allergic rhinitis or hay fever) occur when allergens found outdoors are inhaled into the nose and lungs.

Common allergens are tree pollen in the spring, grass pollen in the summer and weed pollen in the fall, as well as mold spores. Outdoor mold spores peak in July in warmer states and in October in colder states.

A study in the September issue of the journal Annals of Allergy, Asthma and Immunology echoed the impact of climate change on allergies. The study linked increased pollen concentrations and lengthened allergy seasons to warmer temperatures.

The ragweed pollen season has grown as much as 13 to 27 days longer since 1995, found a 2011 study from the U.S. Department of Agriculture. It linked the later end of the season to higher temperatures from climate change.

Weber says that with increased exposure to allergens because of longer pollen seasons, more people may become sensitized. "Older patients are coming in with new onset of hay fever," he says.

About 16.9 million U.S. adults were diagnosed with hay fever in 2011, according to the 2011 National Health Interview Survey. About 6.7 million U.S. children were reported to have hay fever.

Pollen and mold are among the allergens that can trigger asthma attacks.

Asthma, a chronic disease affecting the lungs, causes breathlessness, chest tightness, coughing and wheezing. In 2010, about 18.7 million adults and 7 million children had asthma in the USA, according to the CDC's National Asthma Control Program.

To find out if you have symptoms of allergies or allergic asthma, you can start with an online self-test from the American College of Allergy, Asthma and Immunology.

If you have allergies, treatment includes avoidance of allergens, medication and immunotherapy, such as allergy shots.

Berger, an allergist in Mission Viejo, Calif., says it is important to see a board-certified allergist for diagnosis and treatment. He says having allergies is "a common problem but has a huge impact on quality of life."

Tips for people with allergies

-- Watch the pollen count. If pollen counts are high, you may want to avoid outdoor activities during early morning hours. (You can find pollen levels on allergy relief and weather sites such as AccuWeather.com and the National Allergy Bureau.)

-- When driving, keep your car windows closed.

-- When you're home, keep your bedroom windows closed.

-- Clean your air-conditioning filters regularly.

-- If you've been outdoors, take a shower and wash your hair to get rid of any pollen.